Batboard

I've got two MTX9000 B7 radios. I decided to play with them tonight a bit and found that one of them had an intermittant "whine" (sounds like a pulsed tone) in it's TX audio. If you hold the PTT and smack the radio, it goes away. It's very bad when it happens though. Way beyond just annoying.

Well, since the radio with the nasty audio had a brand new case, I decided - what the hell, I'd rather have the nice case on the radio without the audio squeal.

Low and behold, the squeal followed the new case.

So, now I'm at a loss. It almost has to be RF getting into the audio chain somehow but, I don't know where to even look for a problem.

Has anyone seen this problem before? What do I need to do to make it go away? I'd really like to put these radios into service but, I need two working radios to do it and I definately can't do it with the intermittant squeal on one of them.

John

Thanks to some handy advice from Mancow, my audio problem has been solved.

In case anyone else ever has this problem, this is what I did to fix it:

I resoldered (reheat, add a tiny bit of solder) the chip capacitor that is connected to the mic/speaker flex between the mic and the speaker.

I never noticed that it was even there and not having the service manual, I didn't even know to look for it. It would have jumped right out at me had I known it was there. I had even thought to myself, "I wish I had the schematics for this pig. I'd find somewhere convenient to put a cap across the mic input!"

So, if you have a "whine" on your MTSX audio that sounds like you're getting RF into the audio chain, this is a good spot to look.

John

I've heard a similar whine, but on receive, on GTX-900 portables that also seemed to "go away" when the case (which also includes the speaker/mike/flexcable) got replaced. In this situation it's at a very low level and seems to go away if the signal strength increases or the volume is turned up. Very strange indeed.

Bob M.

This whine was loud enough to drown out the real TX audio about 90%. It was very obnoxious!

John